Revert vendor directory to support old golang (GOPATH mode)

gomodule is still in progress to migrate for now, hence multus
team decide to keep vendor directory to support build without
gomodule.

vendor/github.com/googleapis/gnostic/extensions/extensions.go

@@ -0,0 +1,82 @@
+// Copyright 2017 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package openapiextension_v1
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+
+	"github.com/golang/protobuf/proto"
+	"github.com/golang/protobuf/ptypes"
+)
+
+type documentHandler func(version string, extensionName string, document string)
+type extensionHandler func(name string, yamlInput string) (bool, proto.Message, error)
+
+func forInputYamlFromOpenapic(handler documentHandler) {
+	data, err := ioutil.ReadAll(os.Stdin)
+	if err != nil {
+		fmt.Println("File error:", err.Error())
+		os.Exit(1)
+	}
+	if len(data) == 0 {
+		fmt.Println("No input data.")
+		os.Exit(1)
+	}
+	request := &ExtensionHandlerRequest{}
+	err = proto.Unmarshal(data, request)
+	if err != nil {
+		fmt.Println("Input error:", err.Error())
+		os.Exit(1)
+	}
+	handler(request.Wrapper.Version, request.Wrapper.ExtensionName, request.Wrapper.Yaml)
+}
+
+// ProcessExtension calles the handler for a specified extension.
+func ProcessExtension(handleExtension extensionHandler) {
+	response := &ExtensionHandlerResponse{}
+	forInputYamlFromOpenapic(
+		func(version string, extensionName string, yamlInput string) {
+			var newObject proto.Message
+			var err error
+
+			handled, newObject, err := handleExtension(extensionName, yamlInput)
+			if !handled {
+				responseBytes, _ := proto.Marshal(response)
+				os.Stdout.Write(responseBytes)
+				os.Exit(0)
+			}
+
+			// If we reach here, then the extension is handled
+			response.Handled = true
+			if err != nil {
+				response.Error = append(response.Error, err.Error())
+				responseBytes, _ := proto.Marshal(response)
+				os.Stdout.Write(responseBytes)
+				os.Exit(0)
+			}
+			response.Value, err = ptypes.MarshalAny(newObject)
+			if err != nil {
+				response.Error = append(response.Error, err.Error())
+				responseBytes, _ := proto.Marshal(response)
+				os.Stdout.Write(responseBytes)
+				os.Exit(0)
+			}
+		})
+
+	responseBytes, _ := proto.Marshal(response)
+	os.Stdout.Write(responseBytes)
+}